1. Field of the Invention
This invention relates in general to magnetic recording disk drives and in particular to a magnetic recording disk drive that uses an air-bearing slider for contact recording.
2. Description of the Related Art
In conventional magnetic recording rigid disk drives, each of the read/write transducers (or heads) is supported on an air-bearing slider that rides on a cushion or bearing of air above the surface of its associated disk surface when the disk is rotating at its operating speed. The slider is connected to an actuator by means of a relatively fragile suspension. The suspension includes a gimbal or flexure that supports the slider and allows it to pitch and roll and a load beam with a dimple or tip that applies a small load force at a slider pivot point. The suspension thus applies a load force and a moment about the pivot point to bias the slider toward the disk surface. The slider has an air-bearing surface (ABS) designed to generate an air-bearing force to counteract the bias force from the load beam and thus assure that the slider “flies” above and out of contact with the disk surface.
More recently, continuous-contact recording has been proposed that uses a head carrier in the form of a slider with an ABS that only partially supports the slider above the disk surface, with a rear or trailing portion of the slider that supports the head and remains in contact with the disk surface during reading and writing of data. The interface between this type of continuous-contact slider and the disk has been investigated by J. Itoh, et al., “An Experimental Investigation for Continuous-contact Recording Technology,” IEEE Trans. on Magnetics, vol. 37, No. 4 Jul. 2001, p. 1806. Continuous-contact recording head-suspension assemblies are described in U.S. Pat. No. 6,157,519.
In addition to continuous-contact recording, near-contact recording has been proposed. In near-contact recording the slider or a portion of the slider is in contact with the rotating disk during an initial wear-in period. After a certain amount of wear has occurred the slider then flies with a very small clearance. In near-contact recording, the slider will be in contact with the rotating disk during a significant portion of the time the disk is at its operating speed. U.S. Pat. No. 6,762,909 B2 describes a slider for near-contact recording that has a protrusion pad on its trailing portion that supports the head and partially wears away after an initial wear-in period.
In both continuous-contact and near-contact recording, as well as in conventional non-contact recording, the slider has a positive “pitch” when the disk is rotating at its operating speed. Positive pitch means that the leading portion of the slider, i.e., the “upstream” portion facing the air flow induced by the rotating disk, is farther from the disk surface than the “downstream ” or trailing portion. The read/write head is located on the trailing portion, usually on the rear or trailing surface of the slider, so that it is located close to the disk surface.
A serious problem encountered in contact recording is bounce of the slider caused by friction between the slider and the rotating disk, as described by C. M. Mate et al., “Dynamics of Contacting Head-Disk Interfaces”, IEEE Trans. on Magnetics, vol. 40 (2004) pp. 3156-3158. Several approaches have been shown to work for reducing bounce, but all of them are generally unacceptable. For example, increasing the disk surface roughness increases the magnetic spacing between the head and the recording medium by an unacceptable amount, texturing of the ABS adds more processing steps and can damage the head, and decreasing the mobility of the liquid lubricant on the disk surface can lead to poor durability of the slider-disk interface. The positive pitch slider contributes to the bounce problem because the friction force on the slider is at the downstream or trailing end and thus applies a moment about the slider pivot point that tends to lift the trailing end of the slider off the disk.
Negative-pitch sliders have been proposed for non-contact recording. A negative-pitch slider has at least one point in the leading portion of the slider closer to the disk than any point in the trailing portion of the slider when the disk is rotating at its operating speed. The negative-pitch slider has been shown to have advantages in non-contact recording because of reduced fly height sensitivity to variations in ambient pressure and radial position on the disk. U.S. Pat. No. 6,751,063 B2 describes a non-contact recording disk drive with a negative-pitch slider.
What is needed is a contact recording disk drive that minimizes the problem of slider bounce.